|Irradiation of the lungs via inhalation|
Radon descendants are responsible for a natural source of internal exposure. The lungs are affected when aerosols carrying these radioactive descendants for the radon gas are inhaled. Once deposited on the surface of the lungs, the radioelements emit alpha rays which can penetrate deep enough to reach the cells of the bronchioles sensitive to cancers. The beta rays emitted by tritium (a radioactive isotope of hydrogen produced by cosmic rays) can also reach the lungs, but deposit far less energy.